Skeletal fractures are a major health care concern of elderly populations due to deteriorated bone quality, which is dependent on the properties and spatial arrangement of bone constituents (i.e., mineral, collagen and water). Among them, water has been identified to distribute in bone in three major forms: mobile water (in pores), loosely bound water (attached to mineral and collagen surfaces), and tightly bound water (as part of mineral and collagen molecules). It has been well known that dehydration of bone significantly reduces the toughness of the tissue, suggesting that interactions of water with the other bone constituents (i.e., mineral and collagen) play a significant role in bone toughness. Relevant to clinical concerns, recent findings indicate that the toughening effect of water diminishes with aging, suggesting that age-related changes may somehow block the pathway(s) for water to function as a plasticizer in bone. In general, water molecules may interact with mineral and collagen phases in two major ways: polar interactions (van der Waals forces) and much stronger hydrogen bonds. Thus, it is important to understand how such interactions (polar interaction and hydrogen bond) with the mineral and collagen phases by water are involved in toughening of bone tissues. Previous evidence has shown that the interaction of water with the mineral and collagen phases could inflict significant impacts on the mechanical behavior of bone. To this end, we propose in this exploratory proposal to study the contribution of polar interactions and hydrogen bonding ability of water to the mechanical behavior of bone using a novel experimental design and state-of-the-art techniques. Such understanding will help decipher the role of water in sustaining the toughness of bone and further facilitate the understanding of age-related changes in bone ultrastructure that obstruct the contribution of water to the tissue toughness. The hypothesis of this study is that water molecules affect the interaction between the mineral and collagen phases through both polar interactions and hydrogen bonding, thus imposing a significant effect on the toughness of bone. To test the hypothesis, two specific aims will be addressed: 1) to determine the effect of polar (van der Waals) forces and hydrogen bonding ability of water molecules on the interaction between the mineral and collagen phases;and 2) to determine the effect of polar (van der Waals) interactions and hydrogen bonding ability of water molecules on the mechanical behavior of bone. Combining the results obtained from Aim 1 and 2, the role of water in sustaining the toughness of bone will be elucidated. PUBLIC HEALTH RELEVANCE: Previous evidence has indicated that the role of water in sustaining the toughness of bone diminishes with increasing age. A systematic study using start-of-the-art techniques is proposed to elucidate the toughening mechanism of water to bone at ultrastructural levels. Such understanding will assist elucidate age-related changes in bone ultrastructure and its correlation with age-related bone fractures.